The invention disclosed and claimed herein generally pertains to a method for reducing artifacts in acquired magnetic resonance (MR) images, wherein the artifacts result from translational motion of a patient or other object of imaging. More particularly, the invention pertains to a method of such type wherein the motion is small, in comparison with the spatial resolution of acquired images.
In conventional MR imaging, scan time can typically last from a few seconds to several minutes. During this time, it is very common for translational motion to occur in a body part being imaged, resulting in inconsistent k-space phase errors. MR imaging is very sensitive to such errors, which can cause blurring, ghosting, or other artifacts in a reconstructed image. Translational motion may result from involuntary patient movement or from restlessness, particularly in the case of pediatric patients, and may thus be very difficult to prevent. Such motion tends to be both non-periodic and unpredictable. Accordingly, a technique known in the art as gating, which has been used in the past to compensate for periodic motion in MR imaging, is not useful in connection with translational motion as described above. The gating technique, wherein data acquisition is synchronized with motion, is discussed, for example, by W. J. Rogers, Jr. and E. P. Shapiro in "Effect of RR interval variation on image quality in gated, two-dimensional, Fourier MR Imaging", Radiology, vol. 186, pp. 883-887 (1993).
In another motion correction technique, known as navigator echo correction, an additional echo is acquired in the same pulse sequence that acquires the k-space data. This echo, referred to as a navigator echo, is used to determine the instantaneous position of the object when the sequence is played out, and subsequently to correct the k-space data acquired by the same sequence, or to re-acquire the motion-contaminated k-space data should motion exceed a pre-determined threshold. The navigator technique is described, for example, by R. L. Ehman and J. P. Felmlee, Radiology, vol. 173, pp. 2555-263 (1989), and by Z. W. Fu, et al., Magn. Reson. Med., vol. 34, pp. 746-753 (1995). The use of navigator echoes always requires additional data which can lead to longer imaging time.
In view of the above deficiencies of the prior art, it would clearly be desirable to provide an improved technique for correcting errors in MR imaging which result from non-periodic translational motion, wherein the correction technique is comparatively simple, and does not significantly increase data acquisition.